1. Field of the Invention
The present invention relates to a repulsion type circuit breaker provided with a first movable contact which is opened and closed by an opening/closing mechanism and a second movable contact which is disconnected from the first movable contact by an electromagnetic repulsion force, specifically a contact device which is adapted so that upon extreme current flow disconnection of the second movable contact may not be obstructed by the contact spring which urges the first and second movable contacts together.
2. Discussion of the Related Art
FIGS. 4 and 5 both show the side view of the conventional contact device in a closed condition. In FIG. 4, the first movable contact 1 is pivotably secured to the main casing 2 by the holder (not shown) and driven for opening and closing by the opening/closing mechanism (not shown). The second movable contact 3 which comes in contact with the first movable contact 1 is V-shaped as viewed from the side and is pivotably secured at its corner to the second movable contact support 5 by the pivotal pin 4. The second movable contact support 5 is fixed to the main casing 2 with a screw 6. The second movable contact 3 is electrically connected to a terminal plate 8 at the power supply side with a lead wire 7, and the terminal plate 8 is fixed to the main casing 2 with a screw 9. The contact spring 10 comprises a double tortional twisted coil spring with two arms 10a fixed to the second movable contact support 5, a U-bent part 10b engaged with the second movable contact 3, and a coil 10c between each arm 10a and the U-bent part 10b. The contact spring 10 is mounted about the pivotal pin 4. Thus, the contact spring 10 urges the second movable contact 3 in the clockwise direction toward the first movable contact 1 to maintain a required contact pressure. Contact edges 1a and 3a are provided respectively on the first movable contact 1 and the second movable contact 3.
FIG. 5 shows another example of the conventional contact device in which a compression coil spring used as the contact spring 10 is inserted between the bar type second movable contact 3 and the terminal plate 8. The second movable contact 3 is pivotably secured at its end to the second movable contact support 5 by the pivotal pin 4. Electrical connection between the second movable contact 3 and the second movable contact support 5 is maintained by sliding contact, and between the terminal plate 8 and the second movable contact support 5 by direct connection.
In the configurations shown in FIGS. 4 and 5, the current flows in opposite directions, as shown with arrowheads, in mutually parallel conductive parts of first movable contact 1 and second movable contact 3. An electromagnetic force is created by these currents causing first movable contact 1 and second movable contact 3 to repel each other. The repulsion type circuit breaker uses this electromagnetic repulsion force to turn second movable contact 3 in the counterclockwise direction against contact spring 10 to quickly disengage contact edges 1a and 3a when current flow reaches a predetermined amount. The circuit formed between contact edges 1a and 3a is thereby broken interrupting any large current flow such as a shorting current.
In such a repulsion type circuit breaker, when second movable contact 3 is disconnected by the electromagnetic repulsion force, contact spring 10 still urges the second movable contact 3 in opposition to the electromagnetic repulsion force used to open the circuit. In the case of the conventional circuit breaker, the amount of electromagnetic repulsion force required to overcome, the reactive force of contact spring 10 increases as the spring is compressed. The increasing force required to bend the spring has been a substantial obstacle in reducing the disconnection time of the second movable contact.